Seminar Series Events/Videos

In general relativity, the effective-one-body (EOB) approach, which consists in reducing the two-body dynamics to the motion of a test particle in an effective static, spherically symmetric metric, has proven to be a very powerful framework to describe analytically the coalescence of compact binary systems.

Gravitational waves from the mergers of five binary black holes and one binary neutron star were detected in the past two years by the advanced LIGO and Virgo detectors. These detections allowed our Universe to be observed in gravitational waves for the first time, and they have tested the predictions of general relativity for dynamical and strongly gravitating systems. I will discuss these results and also highlight a few additional examples of ways in which gravitational waves can shed light on open questions in theoretical physics and astrophysics.

The observations of gravitational waves from coalescing compact binary systems allow us to test gravity in its strong field regime. In order to better constrain alternative theories of gravity, one has to build template waveforms for these theories. In this talk, I will present a post-Newtonian Lagrangian approach adapted to the specificities of scalar-tensor theories. I will derive the equations of motion of a compact binary system at 3PN order in harmonic coordinates. This result is primordial in order to compute the scalar and gravitational waveforms at 2PN order.

When two black holes merge, they 'ringdown' as they settle into a final Kerr black hole. The ringdown part of the gravitational wave signal probes the strong field gravity, enabling us to test the general theory of relativity (GR) in that regime. In this talk, I will focus on one particular challenge associated with the ringdown - "When does a ringdown start during a binary black hole merger?". Then I will end the talk with a brief summary of our prospects to perform GR tests with the ringdown signals using the current and future ground-based gravitational wave observatory.

The long-awaited detection of gravitational waves has provided us with another source of information about the Universe. In this talk I will give an overview of how we extract information from gravitational wave signals with a focus on signals for which we do not have a definitive and reliable model for what the signal looks like. In particular I will describe how we can analyze the signal emitted after two neutron stars have merged. I will describe how the information extracted from such a signal can be used to place constrains on the equation of state of dense matter.

The era of gravitational wave detection is upon us. Advanced LIGO (aLIGO) is now in full operation. It has successfully detected the gravitational waves emitted from distant pairs of black holes (BHs) as they spiral together and merge. And we have many more detections to look forward to. But where are these BH-BH mergers happening, in the vast wilderness of the cosmos?

Gravitational wave astronomy provides an unprecedented opportunity to test the nature of black holes and search for exotic, compact alternatives. Recent studies have shown that exotic compact objects (ECOs) can ring down in a manner similar to black holes, but can also produce a sequence of distinct pulses resembling the initial ringdown. These “echoes” would provide definite evidence for the existence of ECOs. In this work we study the generation of these echoes in a generic, parameterized model for the ECO, using Green’s functions.

Models of gravitational waveforms play a critical role in detecting and characterizing the gravitational waves (GWs) from compact binary coalescences. Waveforms from numerical relativity (NR), while highly accurate, are too computationally expensive to produce to be directly used in parameter estimation. We propose a Gaussian process regression (GPR) method to generate accurate reduced-order-model waveforms based only on existing accurate (e.g. NR) simulations.

The characteristics of black holes smaller than the Planck scale are addressed. These result from a modified metric that reproduces desirable aspects of a variety of disparate models in the sub-Planckian limit, while remaining Schwarzschild in the large mass limit. The self-dual nature of this solution has two interesting features: first, it naturally implies the Generalized Uncertainty Principle. Secondly, this metric exhibits an effective dimensional reduction feature, indicating that the gravitational physics of the sub-Planckian regime is effectively (1+1)-D.